1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a semiconductor device. More particularly, the present invention relates to a method and an apparatus for manufacturing a semiconductor device having a barrier layer.
2. Description of the Background Art
Conventionally, a semiconductor device is formed by stacking a plurality of layers each having an interconnection layer. For connecting interconnection layers included in the adjacent layers, first a through hole is formed and then a plug of tungsten or the like is filled in to the through hole. For preventing tungsten diffusion and oxidation, a barrier layer of titanium, titanium nitride or the like is generally formed on bottom and side surfaces of the through hole by sputtering.
In recent years, diameter of the through hole is gradually decreasing along with the miniaturization of the semiconductor device. The depth of the through hole, however, does not become smaller because the thickness of the layers constituting the semiconductor device does not significantly change in spite of the miniaturization of the device. Thus the aspect ratio (a ratio of the depth to the diameter) of the through hole tends to increase.
In a conventional sputtering technique, when the diameter of the through hole is small, a barrier layer is formed only at an upper portion and not on the bottom surface of the through hole. When tungsten is filled in such through hole, aluminum alloy in a lower layer changes its quality at the bottom portion of the through hole, whereby a poor connection or disconnection tends to occur in this area.
Japanese Patent Laying-Open No. 8-127870 addresses this problem by placing a target including a material of a barrier layer a distance as long as 200 mm, away from a silicon substrate on which the barrier layer is to be formed at the sputtering and forming the barrier layer on the bottom surface of the through hole as well.
The method of manufacturing the barrier layer according to the above mentioned layed-open application has the following problems. FIG. 7 is a schematic diagram of a sputtering apparatus referenced for describing the problem of the conventional method. As shown in FIG. 7, in the sputtering apparatus, a silicon substrate 100 and a target 120 of titanium which is a material of the barrier layer are disposed opposite to each other. An interlayer insulation film 101 is formed on silicon substrate 100. A through hole 102 is formed in a central area of interlayer insulation film 101. Additionally a through hole 103 is formed in an outer peripheral area of interlayer insulation film 101. The distance between target 120 and a surface of silicon substrate 100 is about 200 mm.
In the sputtering apparatus with such a configuration, an angle at which the target is viewed from a lower edge of a side surface 102c or 102d of through hole 102 through the opening of through hole 102 is defined as xcex2xc2x0.
In the outer peripheral area of interlayer insulation film 101, an angle at which target 120 is viewed from a lower edge of a side surface 103d on the outer peripheral side of through hole 103 is xcex2xc2x0. An angle at which target 120 is viewed from a lower edge of a side surface 103c on a central side of interlayer insulation film 101 through an opening of through hole 103 is defined as xcex1xc2x0. Here, xcex1xc2x0 is smaller than xcex2xc2x0.
FIG. 8 is a sectional view of a barrier layer manufactured by the apparatus shown in FIG. 7. Referring to FIG. 8, as the angle at which target 120 is viewed from the lower edge of side surface 103c is xcex1xc2x0 which is relatively small as shown in FIG. 7, the number of titanium atoms colliding with side surface 103c becomes small, whereby a barrier layer 104 becomes thinner at side surface 103c and an upper portion 103a of through hole 103. Conversely, as the angle at which target 120 is viewed from the lower edge of side surface 103d is xcex2xc2x0 which is relatively large, the number of titanium atoms colliding with side surface 103d becomes large, whereby barrier layer 104 becomes thicker at side surface 103d and at an upper portion 103b farther from the center of silicon substrate 100. The center of silicon substrate 100 is located in the direction shown by an arrow 110.
When barrier layer 104 is thin at some portions, WF6 gas used for manufacturing a tungsten plug may react with the thin portion of barrier layer 104 in upper portion 103a of the through hole, thereby causing the barrier layer to be peeled off.
An object of the present invention is to provide a method and an apparatus for manufacturing a semiconductor device allowing a barrier layer formation in a lower portion of a semiconductor substrate, such as a bottom portion of a through hole, with the thickness of the barrier being made uniform in an upper portion of the semiconductor substrate, such as an upper portion of the through hole, when the through hole or a recess portion with a large aspect ratio exists.
In accordance with one aspect of the present invention, in a method of manufacturing a semiconductor device, a main surface of a semiconductor substrate and a main surface of a target which is a material of a film to be formed on the main surface of the semiconductor substrate are disposed approximately parallel and opposite to each other, and the film is formed on the semiconductor substrate by sputtering the target material. The method includes the following steps.
(A) Forming a first film by sputtering on the main surface of the semiconductor substrate while maintaining a first distance between the main surface of the target and the main surface of the semiconductor substrate.
(B) Forming a second film by sputtering on and adjacent to the first film while maintaining a second distance shorter than the first distance between the main surface of the target and the main surface of the semiconductor substrate.
According to the method of manufacturing the semiconductor device including such steps, first, in the step (A), as the distance between the target and the semiconductor substrate is the first distance which is relatively long, when atoms of the target are scattered out of the target, the atoms are gravitated until they reach the semiconductor substrate. Therefore velocity component in a vertical direction gradually increases until the atoms reach the semiconductor substrate. As a result, the atoms of the target travel in a direction perpendicular to the extension of main surface of the substrate. Thus, a first layer can be formed as a barrier layer at the bottom surface of the through hole in an interlayer insulation film on the semiconductor substrate, even when the through hole has a large aspect ratio.
In the above step (B), as the distance between the target and the semiconductor substrate is the second distance which is relatively short, atoms of target tend to be scattered and directly reach the substrate in random directions. Therefore the thickness of a second layer as a barrier layer can be made uniform in the upper portion for example, of the through hole.
Preferably the first distance is at least 170 mm and the second distance is at most 80 mm. By setting the first distance at this value, the distance between the semiconductor substrate and the target is made long enough to ensure a vertical velocity component of atoms scattered from the target to become large. Therefore, the barrier layer can surely be formed in the bottom surface, for example, of the through hole. On the other hand by setting the second distance at this value, the distance between the semiconductor substrate and the target becomes short enough to allow random movement of atoms scattered from the target, whereby thickness of the barrier layer can be made uniform in the upper portion of the through hole.
On the semiconductor substrate, an interlayer insulation film having a hole is formed. Preferably, first and second films are formed so as to cover the bottom side surfaces of the hole. Here, the bottom surface and side surfaces of the hole can be surely covered by first and second layers as barrier layers.
In a method of manufacturing a semiconductor device in accordance with another aspect of the present invention, the main surface of the semiconductor substrate and the main surface of the target which is a material of a film to be formed on the main surface of the semiconductor substrate are disposed approximately parallel and opposite to each other, and the film is formed on the semiconductor substrate by sputtering the target material. The method includes the following steps.
(A) Forming a first film by sputtering on the main surface of the semiconductor substrate while maintaining an atmosphere between the main surface of the target and the main surface of the semiconductor substrate at a first pressure.
(B) Forming a second film by sputtering on the first film while maintaining an atmosphere between the main surface of the target and the main surface of the semiconductor substrate at a second pressure higher than the first pressure.
According to the method of manufacturing the semiconductor device having such steps, in the above step (A), the pressure between the target and the semiconductor substrate is at the first pressure, which is relatively low. Therefore, the atoms scattered from the target seldom collide with other atoms and the vertical velocity component of the atoms increases due to the gravity until they reach the semiconductor substrate. As a result, atoms are vertically directed to the semiconductor substrate. Thus a first layer as a barrier layer is formed on the bottom surface of the through hole mentioned above as well.
In the above step (B), as the atmosphere between the target and the semiconductor substrate is at the second pressure, which is relatively high, the atoms scattered from the target are likely to collide with other atoms. Then atoms scattered in random directions from the target still move in random directions when they reach the semiconductor substrate. Thus the thickness of a second layer as a barrier layer is made uniform at the upper portion of the through hole as well.
Preferably, the first pressure is at most 0.5 mTorr and the second pressure is at least 2 mTorr. In this case, by setting the first pressure as mentioned above, the fast pressure becomes low enough to increase the vertical velocity component of atoms scattered from the target, whereby a barrier layer can be surely formed at the bottom portion of the through hole. In addition, by setting the second pressure as mentioned above, the second pressure becomes high enough to allow movement of the atoms scattered from the target in random directions, whereby the thickness of the film at upper portion, for example, of the through hole is made uniform.
On the semiconductor substrate, an interlayer insulation film having a hole is formed. Preferably, first and second films are formed so as to cover the bottom and side surfaces of the hole. Here, the bottom surface and side surfaces of the hole can be surely covered by first and second layers as barrier layers.
In an apparatus for manufacturing the semiconductor device according to the present invention, the main surface of the semiconductor substrate and the main surface of the target which is a material of a film to be formed on the main surface of the semiconductor substrate are disposed approximately parallel and opposite to each other, and the film is formed on the semiconductor substrate by sputtering the target material, the apparatus includes a retainer, a substrate holding unit, a target holding unit, and a distance adjustment unit.
Pressure inside the retainer is reduced. The substrate holding unit provided in the retainer holds the semiconductor substrate. The target holding unit, provided in the retainer, holds the target such that the main surface of the target is approximately parallel and opposite to the main surface of the semiconductor substrate. The distance adjustment unit can adjust the distance between the main surface of the semiconductor substrate and the main surface of the target to one of the first distance for forming a first film on the main surface of the semiconductor substrate and the second distance shorter than the first distance for forming a second film on and adjacent to the first film by moving at least one of the target holding unit and the substrate holding unit.
In thus configured apparatus for manufacturing the semiconductor device, by sputtering while maintaining the relatively long first distance between the target and the semiconductor substrate, the vertical velocity component of the atoms scattered from the target increases until they reach the semiconductor substrate. Thus the number of atoms vertically directed to the semiconductor substrate becomes large. Therefore, a first film as a barrier layer can be formed at the bottom portion, for example, of the through hole. If sputtering is performed while the distance adjustment unit maintains the target and the semiconductor substrate at the relatively short second distance away from each other, atoms scattered from the target in random directions move randomly at the relatively upper portion of the semiconductor substrate. Therefore the thickness of the second layer as a barrier layer can be made uniform at the upper portion, for example, of the through hole.
Preferably, the first distance is at least 170 mm and the second distance is at most 80 mm. In this case, by setting the first distance as mentioned above, the distance between the semiconductor substrate and the target becomes long enough to increase the vertical velocity component of atoms scattered from the target, whereby the barrier layer is surely formed at the bottom portion, for example, of the through hole. In addition, by setting the second distance as mentioned above, the distance between the semiconductor substrate and the target becomes short enough to allow the movement of atoms scattered from the target in random directions, whereby the thickness of barrier layer can be made uniform at the bottom portion, for example, of the through hole.
An apparatus for manufacturing the semiconductor device according to another aspect of the present invention includes first and second sputtering apparatus and a transferring apparatus. The first sputtering apparatus disposes the main surface of the semiconductor substrate and the main surface of the target which is a material of a film to be formed on the main surface of the semiconductor substrate approximately parallel and opposite to each other while maintaining the first distance therebetween, and forms a first film on the semiconductor substrate by sputtering the target material. The second sputtering apparatus disposes the main surface of the semiconductor substrate and the main surface of the target which is a material of a film to be formed on the main surface of the semiconductor substrate approximately parallel and opposite to each other while maintaining the second distance shorter than the first distance therebetween, and forms the second film on and adjacent to the first film by sputtering the target material. The transferring apparatus transfers the semiconductor substrate with the first film from the first sputtering apparatus to the second sputtering apparatus.
In the apparatus for manufacturing the semiconductor device with such a configuration, as the sputtering is performed by the first sputtering apparatus while maintaining the relatively long first distance between the semiconductor substrate and the target, a vertical velocity component of atoms scattered from the target becomes large when they reach the semiconductor substrate due to the gravity. Thus the number of the atoms vertically directed to the semiconductor substrate becomes large and a first layer as a barrier layer can surely be formed at the bottom portion of the through hole.
In addition, as the second sputtering apparatus performs sputtering while maintaining the distance between the target and the semiconductor substrate at the relatively short second distance, atoms scattered in random directions from the target move in random directions at the surface of the semiconductor substrate as well. Therefore, the thickness of a second layer as a barrier layer can be made uniform at the upper portion of the semiconductor substrate. In addition, as the transferring apparatus transfers the semiconductor substrate from the first sputtering apparatus to the second sputtering apparatus, production efficiency of the semiconductor device can be improved.
Preferably, the first distance is at least 170 mm and the second distance is at most 80 mm. In this case, by setting the first distance as mentioned above, the distance between the semiconductor substrate and the target becomes long enough to increase the vertical velocity component of atoms scattered from the target, whereby the barrier layer is surely formed at the bottom portion, for example, of the through hole. In addition, by setting the second distance as mentioned above, the distance between the semiconductor substrate and the target becomes short enough to allow the movement of atoms scattered from the target in random directions, whereby the thickness of barrier layer can be made uniform at the bottom portion, for example, of the through hole.
In an apparatus for manufacturing the semiconductor device in accordance with still another aspect of the present invention, the main surface of the semiconductor substrate and the main surface of the target which is a material of a film to be formed on the main surface of the semiconductor substrate are disposed approximately parallel and opposite to each other, and the film is formed on the semiconductor substrate by sputtering the target material, the apparatus includes a retainer, a substrate holding unit, a target holding unit, and a pressure controlling unit.
Pressure inside the retainer is reduced. The substrate holding unit provided in the retainer holds the semiconductor substrate. The target holding unit, provided in the retainer, holds the target such that the main surface of the target is approximately parallel and opposite to the main surface of the semiconductor substrate. The pressure controlling unit can control the pressure in the retainer such that the pressure is maintained at one of the first pressure for forming a first film on the main surface of the semiconductor substrate and the second pressure higher than the first pressure for forming a second film on and adjacent to the first film.
In the apparatus for manufacturing the semiconductor device thus configured, when sputtering is performed while maintaining a relatively low pressure inside the retainer, atoms scattered from the target seldom collide with other atoms. Therefore the vertical velocity component of atoms reaching the semiconductor substrate is increased. Thus the atoms are vertically directed to the semiconductor substrate and a first layer as a barrier layer can be formed at the bottom portion, for example, of the through hole. In addition, when sputtering is performed while maintaining a relatively high second pressure inside the retainer, atoms scattered from the target are likely to collide with other atoms. Therefore the atoms reaching the semiconductor substrate move in random directions. Thus a second layer as a barrier layer has a uniform thickness at the upper area such as the upper portion of the through hole.
Preferably, the first pressure is at most 0.5 mTorr and the second pressure is at least 2 mTorr. By setting the first pressure low enough, as mentioned above, the vertical velocity component of atoms scattered from the target is increased, whereby a first layer as a barrier layer can surely be formed at the bottom surface, for example, of the through hole. On the other hand by setting the second pressure high enough, as mentioned above, atoms scattered from the target move in random directions, whereby the thickness of the second layer as a barrier layer can be made uniform at the upper portion of the semiconductor substrate.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.